This invention relates generally to gas generating materials such as used in the inflation of inflatable devices such as inflatable vehicle occupant restraint airbag cushions and, more particularly, to ignition enhanced gas generating materials.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an "airbag cushion," that is inflated or expanded with gas when the vehicle encounters sudden deceleration, such as in the event of a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the system, the cushion begins to be inflated, in a matter of no more than a few milliseconds, with gas produced or supplied by a device commonly referred to as "an inflator."
Many types of inflator devices have been disclosed in the art for use in the inflating of one or more inflatable restraint system airbag cushions. Many prior art inflator devices include solid form gas generant materials which are burned to produce or form gas used in the inflation of an associated airbag cushion.
Such inflator devices tend to involve rather complex ignition processes. For example, it is relatively common to employ an electrically initiated squib to ignite a separate charge of an igniter composition. The products of such ignition are then used to ignite the gas generant material. In practice, the ignition process of many various prior inflator devices require such a separate igniter charge because the squib does not itself generally supply sufficient hot gas, condensed phase particles or other ignition products to heat the gas generant material to result in the reaction of the material such as to result in desired gas generation.
As is known, a common means of obtaining substantially simultaneously ignition of an extended length charge of an igniter composition, is by means of an ignition cord. In practice, it is common that such length of ignitor cord be housed or contained within an igniter tube extending within such an igniter charge.
While ignition of the gas generant material may ultimately be achieved through the use of such an igniter charge, such use typically tends to undesirably complicate the ignition process as well as the manufacture, production and design of the associated inflator device. For example, such use necessitates that an igniter composition be manufactured or made and then subsequently handled such as through manufacture of a desired form of container to hold or store the igniter composition for subsequent incorporation into the inflator device design as a part of an igniter assembly.
In addition, the use of such an ignition process can detrimentally impact either or both the weight and cost of the corresponding apparatus hardware. For example, the incorporation and use of such an igniter tube and ignition cord will typically increase both the weight and cost associated with a corresponding assembly.
As will be appreciated, space is often at a premium in modem vehicle design. Consequently, it is generally desired that the space requirements for various vehicular components, including inflatable vehicle occupant restraint systems, be reduced or minimized to as great an extent as possible. The incorporation of an igniter assembly such as described above and associated support structure, may require a larger than desired volume of space within an associated inflator device. In particular, such volume of space could potentially be utilized to store or contain gas generant material and thereby permit the volume of space required by the inflator device to be reduced.
Thus, there is a need and a demand for alternative airbag inflator device ignition schemes and, in particular, there is a need and a demand for avoiding the requirement or inclusion of separate igniter composition charges. Various patents, including U.S. Pat. Nos. 4,698,107; 4,806,180; and 5,034,070, disclose processing wherein an ignition coating is applied, such as in the form of a liquid or a water slurry, to azide-based gas generant materials. Such processing typically necessitates first the formation of the azide-based gas generant, including the proper forming and drying of gas generant grains in selected shapes, followed by the coating of the grain with a wet slurry of the ignition material and then final drying.
As will be appreciated, such processing may involve a greater than desired number of processing steps and associated processing hardware. Thus, there is a need and a demand for a simplified processing technique such as avoids the requirement or inclusion of a separate igniter composition charge.
An oftentimes key performance characteristic of an inflatable restraint system inflator device is termed, "ignition delay," i.e., the period of time between when the system, e.g., the inflator, is first initiated and when the system first produces a measurable pressure output. In inflatable restraint systems, it is generally desirable to control and, if possible, minimize such ignition delays.
Unfortunately, the above-described slurry-formed ignition coated gas generants may experience undesirably lengthened or extended ignition delays upon actuation. Thus, there is a need and a demand for processing and a gas generant such that the gas generant may provide improved performance, such as significantly reduced ignition delays, for example.